1. Field of the Invention
The present invention relates to body tissue-derived Pluripotent stem cells.
2. Background Art
Planarians and newts can regenerate their entire bodies even after their bodies have been cut. Such high regenerative capacity of planarians and newts depends on the presence of pluripotent stem cells existing in the mesenchymal tissues. However, in the case of higher organisms such as humans, the tissue regenerative capacity is far lower than that of those animals. Cells of inner cell mass in a mammalian blastocyst is recognized as pluripotent stem cells that is capable of differentiating into cells of ectodermal, mesodermal, and endodermal cell lineages. However, such broad spectrum of differentiation ability becomes limited as development proceeds, followed by cell differentiation for specialization resulting in each type of tissue, and thus, unlike planarians and newts, pluripotent stem cell are not considered to be residing in the living body of higher mammals.
Bone marrow stromal cell (MSC) fractions are known to having the ability to differentiate into bone, cartilage, adipocytes, neuronal cells and skeletal muscles by induction, and the like have been reported as cells having differentiation potency obtained from an adult (see Non-Patent Documents 1 and 2). However, bone marrow stromal cells (MSCs) are comprised of various cell kinds, and thus cells responsible for the differentiation of MSC fraction are not clearly understood. Furthermore, induction of MSCs requires stimulation with a specific compound, gene transfer, or the like for differentiation of MSCs into specific cells. Specifically, there is a need to construct a system for inducing differentiation.
Furthermore, there have been reported that when MSCs are infused into living body, a small part of MSC fractions are known to home into damaged tissues and differentiate into tissue specific cells and contribute to repair. Such tissue repair was observed in tissues and organs of endodermal-, ectodermal- and mesodermal origins. However, the cells responsible for the repair remained an enigma.
iPS cells (induced pluripotent stem cells) (see Patent document 1, Patent document 2, Non-patent document 3, and the like) have been reported as adult-derived pluripotent stem cells. However, establishment of iPS cells requires an artificial operation using a specific substance, such as introduction of a specific gene into mesenchymal cell fraction (for example, a dermal fibroblast fraction) or introduction of a specific compound into somatic cells. While iPS can generate cell of all three germ layers, their tumorigenicity pose limitation for clinical application.    Patent document 1 JP Patent No. 4183742    Patent document 2 JP Patent Publication (Kokai) No. 2008-307007 A    Non-patent document 1 M. DEZAWA et al., The Journal of Clinical Investigation, 113, 12, pp. 1701-1710, (2004)    Non-patent document 2 M. DEZAWA et al., SCIENCE, 2005 Jul. 8, 309, pp. 314-317, (2005)    Non-patent document 3 Okita K. et al. SCIENCE, 2008 Nov. 7, 322 (5903), pp. 949-953